Hitherto, it has been known that in the rubber industry, at the time of producing a rubber composition containing a filler such as carbon black, a rubber wet master batch is used to improve the composition in workability and improve the filler in dispersibility. This is a matter obtained by mixing the filler and a dispersing solvent with each other beforehand at a predetermined blend ratio, dispersing the filler into the dispersing solvent by mechanical force to prepare a filler-containing slurry solution, mixing this solution with a rubber latex solution in a liquid phase, adding to the mixture a coagulant such as an acid, and then collecting and drying the resultant coagulated product. The use of a rubber wet master batch gives a rubber composition better in filler-dispersing performance, and better in rubber properties such as workability and reinforceability than the use of a rubber dry master batch obtained by mixing a filler with a rubber in a solid phase. The use of such a rubber composition as a raw material makes it possible to produce, for example, a pneumatic tire decreased in rolling resistance and made excellent in fatigue resistance, or other rubber products.
Patent Document 1 listed below describes, as a process for producing a natural rubber wet master batch, a process for producing a natural rubber wet master batch, including the step of mixing a natural rubber latex with a slurry solution in which a filler such as carbon black is beforehand dispersed in water, wherein about the particle size distribution of the filler in the slurry solution, the 90%-by-volume particle diameter (D90) of the particles is adjusted to 30 μm or less. Patent Document 2 listed below describes, as a natural rubber wet master batch rubber composition, a natural rubber wet master batch rubber composition obtained by a producing process of mixing a natural rubber latex with a slurry solution in which carbon black is beforehand dispersed in water.